JP-A-9056991 describes a lifter fixed at the periphery part of a rotary drum and cylindrical seals are fixed at the outer periphery of an air intake plenum and of an air exhaust plenum, so that a circulation passage is formed on the back of the rear wall of the drum. The use of two concentric air plenum chambers and related seals makes the above known solution quite complex and not easy to be implemented. Moreover in the above known solution the process hot air is flowing always and entirely through the lifters, even if the lifters are in an upper position during drum rotation. In this condition, i.e. when the lifters are not in contact with clothes, the effectiveness of having air flowing in the lifter is substantially reduced. Another disadvantage of the above known solution is that it cannot be adapted to traditional dryers where air flow enters the drum from a perforated rear wall and leaves the drum from an aperture placed adjacent the front opening of the drum.